(i) Field of the Invention
The present invention relates to molded articles of a syndiotactic polypropylene and a method for preparing the same. More specifically, it relates to molded articles having excellent transparency and excellent balance between stiffness and impact resistance which are obtained by molding a syndiotactic polypropylene having a high tacticity, its copolymer or a mixture of the homopolymer or the copolymer and an isotactic polypropylene, and to a method for preparing these molded articles.
(ii) Description of the Related Art
A syndiotactic polypropylene has been known for a long period of time. Such a polypropylene is prepared by polymerization at a low temperature in the presence of a conventional catalyst comprising a vanadium compound, an ether and an organic aluminum compound, but the syndiotactic polypropylene prepared by this process is poor in syndiotacticity and has elastomer-like characteristics. Therefore, it is scarcely considered that the thus prepared polypropylene exerts its inherent syndiotactic characteristics. On the contrary, a polypropylene having good tacticity, i.e., a syndiotactic pentad fraction of more than 0.7 has been discovered for the first time by J. A. Ewen et al. which can be obtained by the use of a catalyst comprising a transition metal compound having an asymmetric ligand and an aluminoxane (J. Am. Chem. Soc., 110, 6255-6256, 1988).
On molding the syndiotactic polypropylene or a copolymer of propylene and another olefin having a substantially syndiotactic structure obtained by the above procedure, molded articles having relatively excellent transparency are obtained, but this transparency is still unsatisfactory.